Lift, wheels and tires change avg MPG?

[Birddog]

I got a 6" lift and got rid of the OEM 17" wheels and 31" tires for 20" wheels on 35's. I expected for my MPGs to get worse but...

My truck measures average MPGs driven. When I first started to drive my truck with the lift and bigger wheels and tires I noticed that my average MPGs dropped from 20 MPGs to 18.5 MPGs. I thought to myself, wow I thought it would be worse. Before the week was over it quickly dropped to 13.5 MPGs and as a new week progressed it has climbed to 16.5 MPGs. I knew when I got the larger wheels/tires that the slower rotation and additional weight would affect my MPGs but I never expected such a variation. I can only assume the computer is going through some kind of learning curve. I'm hoping someone with actual knowledge of the system will chime in and give me an answer.

I wanted to put this thread in the lifted section but I think this Tech section might be more appropriate.

 

[boomer135]

Did you ever reprogram for larger the tires?

 

[Birddog]

No. Can that be done without a computer?

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[Knotts89]

It can be done with a tuner

 

[4x4Hemi]

Your dealership can correct it to i believe 34 inch tires or something like that. It wouldnt hurt to get your computer reset by the dealer though, then your computer will learn your transmission timing and everything. Dont be surprised if you get less then 15mpg though

Edit: NVM you have a cummins, you should get way better mileage then 15 haha

 

[White Beauty]

Also if your truck is reading 16.5mpg your actually covering more ground then the truck registers with bigger tires. So your probably still in the 18mpg range.

 

[Birddog]

I'm wondering how far my speedometer is off. If that is corrected everything might just correct itself although if it's not more than 2 mph it might not be worth the cost.

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[Power247]

I'm wondering how far my speedometer is off. If that is corrected everything might just correct itself although if it's not more than 2 mph it might not be worth the cost.

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You might be surprised... This site has a calculator...

Tire Size Calculator

 

[Birddog]

Wow it is more than I expected. Thanks for that link. At least now I have an idea how fast I'm going.

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[Cruizer]

I think when I looked it up, going from 33" to 35" was off at least 5mph at 60mph.

So can the dealer not adjust your speedo for tires over 34"?

 

[Birddog]

I know a guy that specializes in speedometer calibrations. I didn't know that the dealership could adjust the speedo at all. Is what they do electronic or actually gear adjustment [if you know]. 4x4Hemi mentioned that above and included reseting the computer, I don't know if you both meant the same thing.

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[Birddog]

Hey guys! Look what I found! It calibrates speedometers for correct tire sizes from 22.5 - 44 inches in 1/4" increments. I bet that would do it all. I already looked and is available for my truck. It's even available for the 2014 Hemi already in case anyone else is reading this and needs one.

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[Birddog]

Just so people can find it here on this thread I'm going to post my find. I found the same features in a Pro Comp unit for $30 cheaper and I will have it on Monday. I'll post my findings after installation probably not until Tuesday.

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[steadly2004]

I got a 6" lift and got rid of the OEM 17" wheels and 31" tires for 20" wheels on 35's. I expected for my MPGs to get worse but...

My truck measures average MPGs driven. When I first started to drive my truck with the lift and bigger wheels and tires I noticed that my average MPGs dropped from 20 MPGs to 18.5 MPGs. I thought to myself, wow I thought it would be worse. Before the week was over it quickly dropped to 13.5 MPGs and as a new week progressed it has climbed to 16.5 MPGs. I knew when I got the larger wheels/tires that the slower rotation and additional weight would affect my MPGs but I never expected such a variation. I can only assume the computer is going through some kind of learning curve. I'm hoping someone with actual knowledge of the system will chime in and give me an answer.

I wanted to put this thread in the lifted section but I think this Tech section might be more appropriate.

I'm not sure if you're computer is the same since you're diesel, but when I went from 17's to 20's after like 3 week I started to get weird issues where the abs and traction control made the truck almost unusable. Not talking about tire sizes but wheel size. Apparently newer Rams use the wheel sensor for traction control and ABS. A flash from the dealer fixed it.

I know it wasn't a tire size issue because I can change that with the tuner I had.

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[Birddog]

The TPMS sensors that came from the factory are still in use. I bought extended stems and they connected to the original sensors so that shouldn't be a problem for me, or at least hasn't been so far. Since this post my MPGs have climbed to 16 and gone back down to 15.6 but at least now they're hovering in the same area. Since the tires and wheels are larger I realistically should be getting better than 16 because I'm actually covering more ground than the sensors are picking up. I ordered a Pro Comp speedometer calibration unit and should be here early next week. Once I program the new tire size I'm hoping to get back on track or maybe with a CPU it will finish the job.

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[R.L.K.]

So how did the MPG do after calibrating the speedometer ?

I SHOT IT WITH MY P.S.E. EVO MAX !!!!

 

[Birddog]

So how did the MPG do after calibrating the speedometer ?

I SHOT IT WITH MY P.S.E. EVO MAX !!!!

I'm not sure about the speedometer but while I was in my long trip to Alabama (just got back 15 minutes ago) I checked the mpg's manually and it was off by about 1mpg. I need to borrow a calibrated radar gun to check the speedometer. It seems like it's pretty close just by the speed I was traveling in relation to the flow of traffic. The calibration unit I bought is pretty easy to use. Even if the speedometer is 1-3 mph off I think I'm still a winner. I'll post an update to the speedometer as soon as I can find a radar gun.

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[Phylodog]

If you've got an android or iPhone you can probably find a free app that will give you your speed via GPS satellite. I've got one on my droid and it works pretty well.

 

[Birddog]

If you've got an android or iPhone you can probably find a free app that will give you your speed via GPS satellite. I've got one on my droid and it works pretty well.

Thanks for the tip.

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[Birddog]

I downloaded a gps speedometer and the speed was 3mph off. I didn't get to check different speeds to see if it was up and down the entire scale because I was in a rush. I'll check it again in the morning.

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